Injector upgrade 23 Oct 2015 Toshi Higo on

Injector upgrade 23 Oct. 2015 Toshi Higo (on behalf of Injector linac group)

Contents • Beam requirement • Schedule and upgrade scenario • Positron status and near future plan • Emittance related issues • Conclusion 23 Oct. 2015 B 2 GM 2

Based on Miura-Furukawa, B 2 GM in June 2015 Super. KEKB schedule Commissioning is divided into three stages. (phase 1, phase 2, phase 3) Calendar 2015 2016 Power restriction in summer Linac Current plan on going 2017 Power restriction in summer Phase 1 Vacuum Scrubbing Basic machine tuning Phase 3 VXD install w/ QCS w/ Belle II (no VXD) L= 1 1034 cm-2 s-1 (KEKB design) w/o DR low emittance 2 n. C/bunch DR commissioning w/ DR Top-up injection no Top-up inj. B 2 GM Add more RF w/ full Belle II L= 8 1035 cm-2 s-1 Full Current Injection Beam 1 n. C/bunch 23 Oct. 2015 Power restriction in summer Phase 2 w/o QCS, Belle II install w/o Belle II Current=1 A 2018 Power restriction in summer low emittance 4~5 n. C/bunch w/ DR Top-up injection 3

Required beam parameters Stage KEKB Phase-I Super. KEKB Item e+ e- Energy 3. 5 Ge. V 8. 0 Ge. V 4. 0 Ge. V 7. 0 Ge. V Primary e-10 n. C Bunch charge → 1 n. C Primary e- 4 n. C 1 n. C → 0. 2 n. C 1 n. C Primary e-10 n. C → 4 n. C 5 n. C Norm. Emittance ( ) ( rad) 2100 2400 150 100/20 (Hor. /Ver. ) 50/20 (Hor. /Ver. ) Energy spread 0. 125% ± 0. 5% 0. 1% Num. of Bunch / Pulse 2 2 2 Repetition rate 50 Hz Simultaneous top-up injection 3 rings (KEKB e-/e+, PF) 4 rings (Super. KEKB e-/e+, PF-AR) 23 Oct. 2015 B 2 GM 4

What and when to be improved from KEKB to Super. KEKB • Present in late 2015 – Prepare low-emittance electron & positron to be cooled at DR • Phase-I in early 2016 – Supply for initial ring tuning and beam-duct baking – Investigate the strategy for emittance-preserved high charge • Phase-II in 2017 – Gradually improve emittance preservation – Make effort for higher charge • Phase-III in late 2017 – Emittance to be fully minimized with maximum charge 23 Oct. 2015 B 2 GM 5

Thermionic gun @A 1 Upgrades of Injector LINAC Photo-cathode RF gun system < e- beam> Low emittance ( 20 mm mrad) high bunch charge ( 5 n. C) Positron production @14 Positron Damping Ring (DR) Low emittance e+ beam Alignment error tolerance 1. 5 Ge. V (local)=0. 1 mm (global)=0. 3 mm Low emittance preservation BCS ECS PF ECS chicane e+ target Pulsed Quads & Pulsed Steering Magnets PF-AR HER LER Event Timing System and Pulsed Modules • Synchronization for 5 -rings including DR • 200 parameters are switched at 50 Hz each mode • Optics at the downstream of DR is switched by using pulsed magnets Positron Capture Section - Flux concentrator (FC) - Large aperture S-band accel. Structures (LAS) 4 times higher e+ yield 23 Oct. 2015 1. 1 Ge. V e+ Damping Ring circ. 136 m RF gun Thermionic gun (10 n. C primary e-) 3. 5 Ge. V 10 n. C x 2 (prim. e-) 5 n. C x 2 (inj. e-) Collimation @18 B 2 GM 6

Electrons • Electrons – for HER – for making positrons • Development on RF gun for electrons has been much advanced – Targeting ultimately low-emittance, high-charge beam – RF gun cavity seems well developed but operation in full spec is required for actual use. – Considerable work is needed to make stable laser system. • We decided to bring thermionic gun for Phase-I to life – For positron generation and possibly for electrons in phase-I – Thermionic gun and RF gun were set in parallel at A 1 23 Oct. 2015 B 2 GM 7

Miura, Furukawa in B 2 GM in June 2015 Beam Commissioning of RF Gun Operation Condition • Laser: 2 bunch, 25 Hz • RF gun acc. voltage: limited to 6. 5 MV by breakdown (13. 5 MV@design) Target : 5 n. C x=50 mm mrad, y=20 mm mrad @ LINAC end x , y = 10 mm mrad @ Gun Bunch charge just after RF GUN (A 1_C 5) Emittance measurement by Quad-scan (m) 1 week RF GUN 4 n. C/bunch Bunch charge: 3 n. C@Screen Beam size was measured shot by shot. => Position jitter is not included x=49. 2 mm mrad 10% y=26. 2 mm mrad 10% Sort for 3 h (Y, M, D) Screen monitor (t=30 m) Archived 1/10 s Bunch charge stability depends on the laser stability. Ø Measured emittances were higher than target values. Ø Higher horizontal emittance is due to laser incident angle. Yb: YAG Thin-disk cooling by soldering Cu plate was Improved. R. Zhang, TUPWA 071 Laser power increased and stability was also improving. 23 Oct. 2015 Need high acc. voltage of RF gun for small emittance B 2 GM 8

A 1 electron gun area in double-deck configuration Two lines merge 23 Oct. 2015 GR-A 1 GU-AT B 2 GM 9

Out of 6 n. C, 2 n. C was transported through target center hole to linac end Recent electron bunch charge 6 n. C was delivered to target In late January, 2016 Radiation shield at target area will be reinforced Target drive current of 200 n. A at present will be increased to 800 n. A with adding iron shield around target area It allows drive electron with 8 n. C/bunch in 2 bunched at 50 Hz. 23 Oct. 2015 B 2 GM 10

Positron system • For phase-I (without DR) – – – Primary drive electron intensity will be increased Radiation safety under 800 n. A for phase-I will be allowed in late Jan. 2015 Production rate will be increased with using flux concentrator, high solenoid field and large aperture accelerator tube Emittance will be reduced by collimation Big shield is being prepared for radiation safety 23 Oct. 2015 B 2 GM 11

Schematic of positron Capture Section SLED KLY 1 -5 KLY 1 -6 target +FC LAS : Large Aperture S-band structure LAS 14 MV/m deceleration & phase slip & acceleration Large Aperture S-band structure (LAS) Solenoids LAS 10 MV/m acceleration n LAS with SLEDs for sufficient field gradient n breakdown issue of LAS in solenoid field n needs careful RF conditioning 23 Oct. 2015 B 2 GM 12

Kamitani, POSIPOL 2015 Positron intensity achieved in 1 July, 2015 e- 4 n. C e+ 0. 4 n. C Reached h=0. 1 before summer shutdown in this year 23 Oct. 2015 B 2 GM 13

Boosting positron yield and intensity Done with electricity power up Under processing with magnetic field For Phase-I 23 Oct. 2015 B 2 GM 14

Target / FC / LAS / Solenoid Beam Radiation shield FC & TGT LAS & Solenoid • FC drive current capacity was doubled in summer 2015 • Radiation shield will further increased before phase-I in Jan. 2016 FC & TGT 23 Oct. 2015 B 2 GM 15

Struggling against gas burst ES Gas pressure RF power Pressure Drive voltage 24 hours Frequent gas burst prevents FC with solenoid field from higher current operation than half-design. 23 Oct. 2015 Frequent gas burst and vacuum breakdown prevents LAS in solenoid field from higher field operation than 10 MV/m. For both, processing is kept under way. B 2 GM 16

Breakdown(? ) to be understood and suppress RF power for LAS FC current pulse RF Input Normal RF reflected RF transmitted Abnormal Normal pulse A few microsec Trailing half was reduced, showing reduction of inductance. 23 Oct. 2015 Abnormal pulse RF power was reflected back to klystron and interrupting transmission through accelerator tube. B 2 GM 17

Further development on FC FC chamber TGT+FC • Replacement of TGT+FC is under consideration for phase-I. • Complete exchange mechanism of the TGT + FC + LAS may be in hand before Phase-II. 23 Oct. 2015 B 2 GM 18

Positron at present and near future • Positron yield of 10% of drive electron was established. • Higher-charge drive electron makes more positrons. • High voltage cabling and other peripheries are approaching to their final ones. • Frequent gas burst is observed especially with solenoid magnetic field at more than 6 k. A current for FC. • Processing is a bit slow and we need to understand what is happening to overcome this phenomenon and operate at design current. • LAS (Large-aperture S-band) accelerator tubes are also subject to gas burst and sometimes with RF breakdown. More conditioning time is needed to reach the full accelerator field with SLED. • Exchange mechanism of target and FC was designed. • Exchange mechanism of fully replacing FC system is underway for final phase. This makes possible to replace any of the TGT/FC/LAS/Solenoid hard wares. 23 Oct. 2015 B 2 GM 19

Collimation for phase-I • A set of three collimators were prepared for cutting beam tail for DR injection at the end of sector 1. • These can be used for cutting positron beam tail for Phase-I without DR. • Additional shield is being prepared. 23 Oct. 2015 B 2 GM 20

Emittance issue for phase-II and beyond 1. Hard wares aligned on a girder by measuring positon by laser tracker 2. Girder are aligned by using laser PD referred to laser light passage 3. Hard ware alignment are to be smoothly improved by measuring with laser tracker 4. Beam evaluation and evaluation to be integrated in the alignment process 5. Suppression of emittance growth due to the floor movement 23 Oct. 2015 B 2 GM 21

J-ARC Alignment Requirement 120 m B A C Rings 1 2 500 m 3 4 5 < 0. 1 mm: 20 mm·mrad is almost satisfied. > 0. 1 mm: emittance preservation is required by some methods. Requirement Local s < 0. 1 mm Global s < 0. 3 mm 23 Oct. 2015 H. Sugimoto B 2 GM 22

Laser PD system as a reference to align girders 500 m laser line 4 -segmented silicon PD (dia. =10 mm) Manual ON/OFF 23 Oct. 2015 Automatic ON/OFF Linear type 2+8 installed now B 2 GM Foresee more installation considering pendulum type and/or present type as candidate 23

Laser PD measurement Mostly aligned by a year ago, summer in 2014 Horizontal Vertical 23 Oct. 2015 B 2 GM UA _REF PD_2 8 PD_28 PD in automatic measurement system are installed two in autumn last year and eight in Summer this year and more to be installed in this fiscal year _G 6 DA Ver. 24

Laser PD more near expansion joint Horizontal Vertical Ver. Same data as left figure Movement near joint is big. Mover or some passive support structure to be developed. 23 Oct. 2015 B 2 GM 25

Hard ware initial alignment on a girders in sector 3 - 5 Horizontal Vertical First round done to install/assign/measure. From now on, we try to find a series of alignment chances to improve smoothness. the stability of this alignment should be confirmed. Horizontal =34 m 23 Oct. 2015/2/24 Vertical =47 m B 2 GM 26 26

Floor configuration B A Gun DR BCS Expansion joint C 1 ECS 2 3 5 PF e+ target ECS PF-AR HER Laser PD continuous measurement devices 23 Oct. 2015 4 B 2 GM Half a year data in next page 27

Movement in half a year Upstream PD_28_G 6 DA 4. 25 m PD_28_REFUA Downstream Correlation between these two positions. 1. Movement of 1 mm order was observed in half a year. 2. Daily movement is of the order of +/- 0. 15 mm. 3. Positive correlation was observed. 23 Oct. 2015 B 2 GM 28

Status and near future strategy • Monthly measurement of relevant PD’s are kept in best effort base for more than a year. • Continuous PD measurement at 10 points are in progress and acquire data over a year. • More automatic PD’s will be made and installed. • Movement at joint is underway to understand movement. • Beam study will be performed to acquire the feasibility of floor movement information by beam. • Feasibility of mover will be studied in mechanism, time, cost. • These efforts should be integrated to make a system before Phase-III, in two years from now. 23 Oct. 2015 B 2 GM 29

Conclusion • Phase-I beam, both electrons and positrons, can be delivered in time in 2016. – Thermionic gun, positron production, shield reinforcement, …. • Preparation for DR will be made by next summer and supply “low” emittance beam will be delivered in Phase-II from 2017. – RF-gun, LTR/RTL, pulse magnet, …. . • Floor movement should be understood and we develop a suppression / compensation scheme to meet Phase-III operation in 2018. – Floor movement and emittance control, ultimate laser RF-gun, … 23 Oct. 2015 B 2 GM 30

Mt. Tsukuba Thank you Super. KEKB dual rings PF-AR PF 23 Oct. 2015 Injector Linac B 2 GM 31